Loss of forests reduce rainfall, cutting into generation potential.

The deforestation of the Amazon is often referred to in terms of the loss of habitat and species. But it also may come back to cause unforeseen problems for us humans, based on a new study in PNAS. Most models of future hydropower productivity have assumed deforestation will lead to increased water runoff, which will in turn increase the amount of power that existing projects will generate. But the study suggests that the feedback between forests and rainfall will ultimately lead to a prolonged and more intense dry season, leaving hydroelectric plants generating less power.

Hydropower is a major contributor of renewable electricity in South America. 100 percent of Paraguay's electricity comes from hydro, and it's a major exporter of power. Brazil isn't far behind, meeting 80 percent of its electrical needs using hydropower, and with several major projects still in the works.

The study focuses on one of these projects which will tap into the potential of the Xingu river basin. A series of damns and hydroelectric facilities in the basin are slated to fill 40 percent of the increase in generating capacity that Brazil expects to need by the end of the decade.

Currently, estimates for its future production are that it will rise due to deforestation. That's because trees and other plants are very good at extracting moisture from the soil but not as good at retaining it in their leaves. The process by which ground water is released as water vapor by the leaves of plants is called evapotranspiration. Estimates are that the loss of forest will reduce evapotranspiration, raising the future production of electricity by the Xingu project by anywhere from four to 12 percent, depending on the degree of forest loss.

But the reduction of evapotranspiration isn't the only affect that cutting down forests will have. In recent years studies have found that tropical rainforests are a self-reinforcing system. The heavy rains enable forest growth and the forest itself feeds back in a way that encourages further rainfall.

Modeling this feedback, the authors show that a deforestation rate of 15 percent will drop the runoff in the Xingu by anywhere from six to 13 percent. If deforestation reaches 40 percent, then the declines will be dramatic, most probably over 30 percent. The declines won't be evenly distributed over the calendar, however, and will largely have the effect of prolonging the dry season, a time when the hydroelectric plants will largely be idle. (The project is only expected to be producing electricity at 40 percent of its potential capacity because of this.)

Overall, the authors calculate that the current rate of deforestation will drop the project from this 40 percent figure down to about 35 percent of electricity-generation capacity. That may not seem like much, but it represents about three percent of Brazil's total current capacity.

And things could potentially get even worse. The large construction project is attracting people to the area, which may increase the rate of deforestation. A number of climate models show the Amazon as a whole will get substantially drier as the century progresses, and the severe droughts of 2005 and 2010 seem to point in that direction as well. If these trends continue, the future could be even worse for the project.

Aside from having large practical implications, the paper's a nice example of how we can integrate more recent findings—the forest-cloud feedback—into existing models, and come out with what we hope is a slightly more accurate answer.

Promoted Comments

For people wanting to know more:here is a youtube presentation by one of the authors of the paper discussed in this article. It starts with some context on the amazon rainforest and then discusses many of the same things in the article, but in more detail.

Thanks John, for an article highlighting an often forgotten negative side effect of deforestation. There's a definite limit to how much forest land we want to turn into crop land.

Increased runoff and flooding as one side effect of deforestation and reduced rainfall as another significant, negative effect, with some degree of aridity or desertification being a worst case outcome in some locals. Not a pretty picture.

Deforestation of the Amazon is also obliterating our planet's biggest carbon sink (correct me if I'm wrong on that). Also fewer trees means less oxygen being produced, so you would think that increases the PPM of CO2, which is now at an all-time (in human history, anyway) high.

I'm jaded by living in Houston Texas. When I hear the term 'GDP growth' I imagine strip malls, exhaust clouds and cement deserts all held together with low-wage jobs that are basically indiscernible from serfdom. So when I read about Brazil's economy skyrocketing, I get this awful feeling that rainforests aren't long for this world.

I'm jaded by living in Houston Texas. When I hear the term 'GDP growth' I imagine strip malls, exhaust clouds and cement deserts all held together with low-wage jobs that are basically indiscernible from serfdom.

That is hyperbole, of course, but it raises an intriguing possibility for economic policy. If we ban people from quitting their jobs and, in fact, ban them from leaving company property for any reason whatsoever, then we wouldn't have any more ruinous wage-inflation and America could get on with the business of business.

Deforestation of the Amazon is also obliterating our planet's biggest carbon sink (correct me if I'm wrong on that). Also fewer trees means less oxygen being produced, so you would think that increases the PPM of CO2, which is now at an all-time (in human history, anyway) high.

The slack-jawed people that downvoted you don't realize that the Amazon is pretty much the lung of the world and humans are the cancer infesting it.

Warming climate will lead to less precipitation in the Amazon basin. If things continue unchecked the Amazon river will lose most of its water volume and the entire region will turn into a savannah.

I totally agree. But of the two problems, deforestation in the Amazon is much more acute.And it's something that if we wanted to mitigate we could. Now!In the next 5 to 10 years the Amazon may totally disappear. We are talking 20% of the world oxygen supply. Do you think if that happens, people are going to be worried about long term global warming? Ha!

Warming climate will lead to less precipitation in the Amazon basin. If things continue unchecked the Amazon river will lose most of its water volume and the entire region will turn into a savannah.

I totally agree. But of the two problems, deforestation in the Amazon is much more acute.And it's something that if we wanted to mitigate we could. Now!In the next 5 to 10 years the Amazon may totally disappear. We are talking 20% of the world oxygen supply. Do you think if that happens, people are going to be worried about long term global warming? Ha!

I'm pretty sure once they see first hand the results of deforestation a few things will happen.

1) An extremist group will spawn and use terrorism to get their point across. These efforts will utterly backfire as the US goes to war with them. The war will be every bit as haphazard as what occurred recently. Expect large scale disruption of any country the extremist attempt to take shelter in regardless of whether those countries give their blessing.

2) The companies the triggered the series of events will simply move on to another huge forest to begin tearing it down. It's obvious to see the major players today are so blinded by greed that they couldn't care less about anything but themselves and maybe their family.

3) More composite materials will make their way into the marketplace aimed at replacing wood. Cost however will remain prohibitive for majority of people in the world. Have you ever priced wood-plastic composite deck boards? It's $15 for 8ft by 5.5in by 1in top board, $25 for 8ft by 10inch by 1inch face board. High quality pressure treated wood of the same size cost 25% of that price, look nicer, and is much more resistant to warping if sufficient quantity of screws are used.

4) Despite it being easier than ever to become entirely paperless, we'll only see more token gestures that don't last long. I was once under the delusion that having a generation grow up with computers would solve this particular problem, but it's just not happening because the previous generations are so damn resistant to change that they are passing on their bad habits.

3) More composite materials will make their way into the marketplace aimed at replacing wood. Cost however will remain prohibitive for majority of people in the world. Have you ever priced wood-plastic composite deck boards? It's $15 for 8ft by 5.5in by 1in top board, $25 for 8ft by 10inch by 1inch face board. High quality pressure treated wood of the same size cost 25% of that price, look nicer, and is much more resistant to warping if sufficient quantity of screws are used.

The vast majority of construction lumber comes from forest plantations (tree farms), not virgin forest, and is renewable and sustainable to a degree similar to that of other farmed agricultural products.

Quote:

4) Despite it being easier than ever to become entirely paperless, we'll only see more token gestures that don't last long. I was once under the delusion that having a generation grow up with computers would solve this particular problem, but it's just not happening because the previous generations are so damn resistant to change that they are passing on their bad habits.

That's not the reason. Paper is simply more convenient than the alternatives right now. There has indeed been a drop in paper usage in many areas, however the ease and convenience of using paper has been greatly improved by computer technology, making it easier and cheaper than ever before for people to waste paper. Oh yeah... almost all paper is also sourced from farmed wood and/or recycled materials, so paper isn't causing the clear cutting of virgin forest either.

Deforestation of the Amazon is also obliterating our planet's biggest carbon sink (correct me if I'm wrong on that). Also fewer trees means less oxygen being produced, so you would think that increases the PPM of CO2, which is now at an all-time (in human history, anyway) high.

re: Carbon Sink

It is my understanding that the Oceans are actually the largest Carbon Sink(s)

(And no I did not down vote you. I consider comment voting to be irrelevant to open discussion.)

"But the study suggests that the feedback between forests and rainfall will ultimately lead to a prolonged and more intense dry season, leaving hydroelectric plants generating less power.

You silly bird, who the heck thinks "long term" consequences these days when those power plants can perceptively benefit from the "short term" results such as a little more turbine spinning water. Besides, deforestation protects the damn from the beavers (power terrorists) building one upstream since they won't have any material. Just keep asking yourself, "How can I maximize potential today".

I can assure you of one thing, you'll never be hired as a Federal Reserve Banker nor a politician with that long sighted attitude; so keep your day job.

Everyone knows that the Amazon is absolutely essential to the well-being of us all. So why isn't drastic measures being taken to take care of the Amazon?

How about something like this: The international community pledges to give the countries in the Amazonas X billion dollars every year. And in return they pledge to not only halt the deforestation 100%, but actually star re-planting the forest. If they fail to stop the deforestation (this can be monitored with satellites), the yearly tribute is withheld, and they could be hit with sanctions as well.

Make it worthwhile for the countries to preserve the Amazon. Make it expensive for them to harm the Amazon. Right now it seems that everyone, including the countries in the Amazonas, know how important the Amazon is, but they still think "Yeah, but if we could just build this one more road... And raze just a bit more space for our cattle...". No, it needs to stop. Completely. Right now.

For people wanting to know more:here is a youtube presentation by one of the authors of the paper discussed in this article. It starts with some context on the amazon rainforest and then discusses many of the same things in the article, but in more detail.

Everyone knows that the Amazon is absolutely essential to the well-being of us all. So why isn't drastic measures being taken to take care of the Amazon?

How about something like this: The international community pledges to give the countries in the Amazonas X billion dollars every year. And in return they pledge to not only halt the deforestation 100%, but actually star re-planting the forest. If they fail to stop the deforestation (this can be monitored with satellites), the yearly tribute is withheld, and they could be hit with sanctions as well.

I think it would just be better for the UN to declare that the Amazon basin is the inheritance of humanity and no longer a sovereign territory of Brazil. If Brazil doesn't agree to hand it over to UN administrators within 90 days, the UN can raise an invasion army to take the Amazon basin away from those irresponsible half-witted hotbloods in Brazil and hand it over to the administration of cool and competent European technocrats.

Everyone knows that the Amazon is absolutely essential to the well-being of us all. So why isn't drastic measures being taken to take care of the Amazon?

How about something like this: The international community pledges to give the countries in the Amazonas X billion dollars every year. And in return they pledge to not only halt the deforestation 100%, but actually star re-planting the forest. If they fail to stop the deforestation (this can be monitored with satellites), the yearly tribute is withheld, and they could be hit with sanctions as well.

I think it would just be better for the UN to declare that the Amazon basin is the inheritance of humanity and no longer a sovereign territory of Brazil. If Brazil doesn't agree to hand it over to UN administrators within 90 days, the UN can raise an invasion army to take the Amazon basin away from those irresponsible half-witted hotbloods in Brazil and hand it over to the administration of cool and competent European technocrats.

[quote=&quot;[url=http&#58;//arstechnica&#46;com/civis/viewtopic&#46;php?p=24491149#p24491149]ws3[/url]&quot;]If Brazil doesn't agree to hand it over to UN administrators within 90 days, the UN can raise an invasion army to take the Amazon basin away from those irresponsible half-witted hotbloods in Brazil and hand it over to the administration of cool and competent European technocrats.[/quote]Come to think of it, there's a better idea:

Um, "slightly"? Unless I read the article wrong, didn't it say that the previous model showed Deforestation = More Hydro Energy, and the improved model says "Deforestation = Less Hydro Energy"? Or maybe you were just being cute.

Everyone knows that the Amazon is absolutely essential to the well-being of us all. So why isn't drastic measures being taken to take care of the Amazon?

How about something like this: The international community pledges to give the countries in the Amazonas X billion dollars every year. And in return they pledge to not only halt the deforestation 100%, but actually star re-planting the forest. If they fail to stop the deforestation (this can be monitored with satellites), the yearly tribute is withheld, and they could be hit with sanctions as well.

I think it would just be better for the UN to declare that the Amazon basin is the inheritance of humanity and no longer a sovereign territory of Brazil. If Brazil doesn't agree to hand it over to UN administrators within 90 days, the UN can raise an invasion army to take the Amazon basin away from those irresponsible half-witted hotbloods in Brazil and hand it over to the administration of cool and competent European technocrats.

The free market approach is for the land owners to sell carbon credits for each acre of forest, and to buy carbon credits for each acre that is cleared.

This an even worse outcome than the already endemic problem. Poor people practice 'slash and burn' agriculture. After a couple of years the soil is depleted, 'rince and repeat' in other words cut down & burn more jungle and abandon the now unproductive 'farm'. Eventually it become grassland, the jungle does not grow back. Then ranchers take it over to grow more beef for McDonalds.

So, let's see...humorous mention of one of the poster boys of environmentalism while commenting on an environmental article is "irrelevant"...while meantime profanity laced ad-hominem attacks regularly go unmoderated. OK...

All this in a comment thread on an article which reaches the "surprising" conclusion that deforesting the Amazon basin is a bad idea. I wonder how many taxpayer dollars were wasted on that particular boondoggle (a detail that goes unmentioned in the article). Despite my love of science, I have sympathy for those in Congress who'd rather not see tax dollars wasted on such things, another random example being Interior Department Spends $472,150 to Train Fish to ‘Recognize and Avoid Predators’.

As far as the Amazon goes, though, I'm sure next-gen nuclear reactors will be more than capable of making up for hydropower shortfalls without generating a single gram of CO2. That is, of course, if the modeling pans out. If it works as well as the current suite of IPCC climate models, a Magic 8-Ball might be preferable.

I totally agree. But of the two problems, deforestation in the Amazon is much more acute.And it's something that if we wanted to mitigate we could. Now!In the next 5 to 10 years the Amazon may totally disappear. We are talking 20% of the world oxygen supply. Do you think if that happens, people are going to be worried about long term global warming? Ha!

First of all, "the Amazon" won't disappear. Perhaps most of the rainforest will though.

Second of all, just to provide a little balance to the breathless hype:

Amazingly, despite all the attention this area receives, I couldn't find any paper or article that examines whether the Amazon is a net consumer or producer of greenhouse gasses. It is true that it converts a good bit of CO2 to oxygen.

So, let's see...humorous mention of one of the poster boys of environmentalism while commenting on an environmental article is "irrelevant"...while meantime profanity laced ad-hominem attacks regularly go unmoderated. OK...

Moderation and official warnings are supposed to provide a bit of a hint: stop saying things that aren't relevant to the discussion and are likely to start an argument - that's trolling, and against the posting guidelines that are linked on every discussion page. I'll link them again, since you don't seem to have read them:http://arstechnica.com/staff/2000/01/postguide/

I suggest that you probably haven't read them because, if you'd scroll down and look at item 6, you'd see the following:"Please respect and abide by the decisions of the moderators. Self-explanatory. If you have issues with moderation, we want to hear about them, but the thread where the moderation took place isn't the place."

And instead you're complaining about moderation here. So, i checked with my fellow moderators, and this now gets you a one-day ban. Next offense will be a week.